1. Field of the Invention
The present invention relates to a color imaging element and an imaging device, and, more particularly, to a color imaging element which can reduce occurrence of color moire and which can realize high resolution, and an imaging device using this color imaging element.
2. Description of the Related Art
In a single plate color imaging element, because a single color filter is provided on each pixel, each pixel has only color information of a single color. Therefore, an output image of the single plate color imaging element is a RAW image (mosaic image), and, thus, processing (de-mosaic processing) for interpolating a pixel of a missing color with peripheral pixels is performed to obtain a multichannel image. In this case, there is a problem in reproduction characteristics of an image signal of a high frequency, and because, with color imaging elements, aliasing is more likely to occur in the taken image than with black-and-white imaging elements, realizing high resolution by expanding a reproduction band while suppressing occurrence of color moire (false color) is an important issue.
Because a primary color Bayer array which is a color array of the color filters most-widely used in the single plate color imaging element is an array in which green (G) pixels are arranged in a checkerboard design and red (R) and blue (B) pixels are arranged in a line-sequential manner, there is a problem in reproduction precision upon generation of a high frequency signal in which a G signal is in a diagonal direction and R and B signals are in horizontal and vertical directions.
When a black-and-white vertically-striped pattern (high frequency image) as shown in FIG. 25(A) is incident on color imaging elements having color filters with a Bayer array shown in FIG. 25(B), if colors are compared by being sorted by the color Bayer array, as shown in FIGS. 25(C) to 25(E), R becomes a light plain color image, B becomes a dark plain color image, and G becomes a gray-scaled mosaic color image, and thus an image which should have originally been a black-and-white image, and which should not have included a difference in concentration (difference in level) among R, G and B, is colored depending on a color array and an input frequency.
In a similar manner, when a diagonal black-and-white high frequency image as shown in FIG. 26(A) is incident on imaging elements having color filters with a Bayer array shown in FIG. 26(B), if colors are compared by being sorted by the color Bayer array, as shown in FIG. 26(C) to 26(E), R and B become light plain color images, and G becomes a dark plain color image, and if a value of black is set to 0, and a value of white is set to 255, because only G is 255 in the diagonal black-and-white high frequency image, the diagonal black-and-white high frequency image becomes green. In this way, it is impossible to correctly reproduce a diagonal high frequency image with the Bayer array.
Typically, in an imaging device using a single plate color imaging element, a high frequency is avoided by disposing an optical low-pass filter comprised of birefringent substance such as a crystal on the front of the color imaging element so that the high frequency is optically removed. However, such a method has a problem that while it is possible to reduce coloring due to folding of a high frequency signal, resolution degrades as its adverse effect.
To solve such a problem, there has been proposed a color imaging element in which a color filter array of the color imaging element is arranged in a three-color random array which satisfies an array restriction condition that an arbitrary target pixel is adjacent to three colors including a color of the target pixel at any of four sides of the target pixel (Japanese Patent Application Laid-Open No. 2000-308080; PTL 1).
Further, there has been proposed an image sensor (color imaging element) with a color filter array, which has a plurality of filters with different spectral sensitivity, and in which, among the filters, a first filter and a second filter are alternately arranged in one of diagonal directions of a pixel lattice of the image sensor in a first predetermined cycle and are alternately arranged in the other of the diagonal directions in a second predetermined cycle (Japanese Patent Application Laid-Open No. 2005-136766; PTL 2).
Still further, there has been proposed a color array of a color solid-state imaging element (color imaging element) having three primary colors of RGB, in which sets of three pixels of horizontally arranged R, G and B are arranged while the sets are displaced in a zig-zag manner in a vertical direction, so that probabilities of appearance of RGB are made equal and an arbitrary line (horizontal, vertical or diagonal line) on the imaging face is made to pass all the colors (Japanese Patent Application Laid-Open No. 11-285012; PTL 3).
Yet further, there has been proposed a color imaging element in which among the three primary colors of RGB, R and B are arranged every third pixel in a horizontal direction and in a vertical direction, and G is arranged between R and B (Japanese Patent Application Laid-Open No. 8-23543; PTL 4).